Telomerase and the maintenance of chromosome ends

The catalytic subunit of telomerase has recently been identified in diverse eukaryotes and shown to be a reverse transcriptase. Ectopic expression of this protein in normal human cells leads to lengthened telomeres-and an ext ended in vitro life span. Other proteins that modulate telomerase activity in vivo are also being identified, including a functionally conserved famil y of proteins with Myb-like DNA-binding domains and proteins that are invol ved in DNA double-strand break repair.